Pioneers of Plasma Cosmology
Kristian Birkeland (1867-1917)
Irving Langmuir (1881-1957)
Hannes Alfvén (1908-1995)
More than 100 years ago, Norwegian physicist Kristian Birkeland proposed an electrical explanation of the auroras, based on direct experimental evidence. He designed a magnetized sphere suspended in a vacuum to experimentally model the electrical behavior of the Earth. He called this experiment a ‘Terrella,’ Latin for ‘little earth.’ He found that the magnetic field of the Terrella guided charged particles to its magnetic poles, producing rings of light that appeared to mimic Earth’s auroras.
Birkeland proposed that auroras are caused by charged particles ejected from the Sun and guided to the Earth’s polar regions by the geomagnetic field. The hypothesis was disputed for many years.
Confirmation of Birkeland’s aurora theory finally came from observations made above the ionosphere by satellites, beginning in 1963. The first map of ‘Birkeland currents’ in the Earth’s polar region was developed in 1974 from satellite-borne magnetic field observations.
Today, Birkeland’s description of current flow in plasma is essential to the understanding of space plasma.
The work of Irving Langmuir left its mark on many sciences. He was largely responsible for the perfection of Edison’s incandescent light bulb. His sonar system for detecting submarines was a vital tool of the allies in World War II, and his understanding of oil films on water or glass surfaces led to dramatic improvements in optics and a Nobel Prize in 1932.
In 1927, Langmuir’s studies of electrical discharge phenomena led him to use the term plasma to describe ionized gases and their lifelike responses to electricity. His observation of the cellular ‘sheath’ that forms around charged objects in a plasma laid a foundation for a new understanding of the ‘magnetospheres’ of planets and stars. Today, ‘Langmuir probes’ in spacecraft continue to expand our understanding of plasma in space.
Virtually all of modern plasma physics is indebted to Hannes Alfvén for his insights into the role of electric and magnetic fields in plasma.
But there is an irony to Alfvén’s contributions. In his earliest papers, he spoke of magnetic fields being ‘frozen’ into plasma, a notion to which astrophysicists were readily attracted, and today the concept underpins most mainstream ideas about magnetic fields in space. Alfvén, however, later dissociated himself from his own pioneering contribution. Instead of isolated magnetic regions enduring forever, he came to see electric currents through the rarefied plasma of space as the source of localized magnetic fields. Based on these observations he and his colleagues proposed a far-reaching alternative cosmology to the Big Bang.
In 1970 Alfvén received the Nobel prize for his “fundamental discoveries in magnetohydrodynamics.” He used the occasion of his acceptance speech to beg scientists to ignore his earlier work. He considered the failure of physicists to produce controlled fusion, after 30 years’ of expensive attempts, to be a result of the tenacity with which they hold on to his mistaken early speculation.